A conventional television system, such as a system in accordance with the NTSC broadcast standard adopted in the United States and elsewhere, processes a television signal representative of an image with a 4:3 aspect ratio (the ratio of the width to the height of a displayed image). Recently, there has been interest in using higher aspect ratio images for television systems, such as 5:3, 16:9 and 2:1, since such higher aspect ratios more nearly approximate or equal the aspect ratio of the human eye compared to the 4:3 aspect ratio of a standard television display. Advanced television systems for producing 5:3 aspect ratio images are described, for example, in U.S. Pat. No. 4,816,899--Strolle, et al. and in U.S. Pat. No. 4,855,811--Isnardi. In these systems side panel image information is encoded by time compressing low frequency side panel luminance and chrominance information into horizontal overscan regions, and high frequency side panel luminance and chrominance information are encoded by time expansion and modulation of an auxiliary subcarrier. The side panel luminance information component (Y) and the side panel chrominance color difference information components (I and Q) are each processed separately before being encoded.
Separate processing of the side panel luminance component, the side panel "I" color difference component and the side panel "Q" color difference component advantageously permits each component to be uniquely tailored with respect to one or more desired factors such as noise reduction, gain, or filter characteristics for example. Illustratively, in the case of a widescreen television signal which is intended to be compatible with a standard NTSC receiver, gain factors could be individually adjusted to assure that side panel information encoded in a broadcast NTSC compatible signal will not produce visible interference in a standard receiver display. Also, the type of noise reduction system employed could be optimized based upon the characteristic of the particular component, e.g., based upon whether or not a given component contains DC information.
It is herein recognized, however, that it can be beneficial to process certain side panel components together as a combined signal before encoding, particularly in a system employing complementary noise reduction apparatus at the transmitter encoder and receiver decoder. Specifically, it is recognized herein that bandwidth restrictions on certain components such as side panel components can lead to unwanted band-edge crosstalk between such components. That is, bandwidth limitations may not permit practical filters from keeping the components sufficiently separated at their band edges to prevent significant crosstalk. This crosstalk can significantly impair the effectiveness of the encoder/decoder noise reduction apparatus, which to be most effective requires that the signal processed by the decoder noise reduction apparatus be essentially the same signal processed by the encoder noise reduction apparatus, except for transmission noise which the noise reduction apparatus is intended to reduce. It is also recognized herein that non-linearities generated by non-linear noise reduction apparatus can create harmonics which can adversely affect the quality of a reconstituted image signal when such components are processed in separate signal paths with separate noise reduction apparatus. The disclosed apparatus according to the principles of the present invention addresses these concerns. In addition to exhibiting a simplified configuration, the disclosed apparatus significantly reduces the impact of the described crosstalk and non-linearities in a reconstituted image signal.